WIP Upgrade govuk_publishing_components

- upgrade to last version before the more complex switch to govuk-frontend v5
- update manifest files and Sass to compile all CSS into one file
- remove print stylesheet as no longer relevant
- update Sass variables/mixins for newer govuk-frontend

Gemfile

@@ -11,7 +11,7 @@ gem "elasticsearch-rails", "~> 7.2.1"
 gem "faraday"
 gem "faraday_middleware"
 gem "govuk_elements_rails"
-gem "govuk_publishing_components", "~> 28.7.1" # TODO: Revert https://github.com/alphagov/datagovuk_find/pull/1286 once 39.2.3+
+gem "govuk_publishing_components", "~> 39.2.0" # TODO: Revert https://github.com/alphagov/datagovuk_find/pull/1286 once 39.2.3+
 gem "htmlentities"
 gem "jbuilder"
 gem "jquery-rails"